Electrodeposition of gold alloys

ABSTRACT

AN AQUEOUS GOLD ALLOY PLATING BATH FOR THE ELECTRODEPOSITION OF GOLD AND ONE OR MORE METALS SELECTED FROM GROUPS II-B THROUGH VI-B OF THE PERIODIC TABLE OF MENDELYEEV AND A METHOD FOR SAID CODEPOSITION. THE USE OF A SOLUBLE ANODE OF THE ALLOYING METAL IN THE CODEPOSITION OF GOLD WITH THAT METAL, ALONG WITH ONE OR MORE OTHER METALS FROM GROUPS II-B THROUGH VI-B IS DESCRIBED. THE PREFERRED ALLOY IS TIN-LEAD-GOLD.

United States Patent 3,764,489 ELECTRODEPOSITION OF GOLD ALLOYS Franco Znntini, Andre Meyer, and Pierre Antony, Geneva, Switzerland, assignors to Oxy Metal Finishing Corporation, Warren, Mich.

No Drawing. Continuation-impart of abandoned application Ser. No. 880,950, Nov. 28, 1969. This application Mar. 27, 1972, Ser. No. 238,473

Int. Cl. C23b 5/42 US. Cl. 20443 G 13 Claims ABSTRACT OF THE DISCLOSURE An aqueous gold alloy plating bath for the electrodeposition of gold and one or more metals selected from Groups II-B through VI-B of the Periodic Table of Mendelyeev and a method for said codeposition. The use of a soluble anode of the alloying metal in the codeposition of gold with that metal, along with one or more other metals from Groups II-B through VI-B is described. The preferred alloy is tin-lead-gold.

This is a continuation-in-part of application Ser. No. 880,950, filed Nov. 28, 1969, now abandoned.

This invention relates to a method and composition for the electrodeposition of alloys of gold with one or more metals. The metals to be codeposited with gold are those of Groups II-B through VI-B of the Mendelyeev Periodic Table of the Elements. The present invention also relates to the electrodeposition of a lead-tin-gold alloy and to the plating bath used for this purpose.

It is an object of the present invention to provide a method and composition by means of which gold alloys having good mechanical characteristics, good resistance to corrosion due to oxidation or chemical agents can be produced.

It is a further object of this invention to obtain an alloy of gold having a gold content of approximately 60% to 85% by weight which will provide electrical, protective and decorative characteristics comparable to that of more pure gold deposits.

It is another object of this invention to increase the efficiency of the plating solution and minimize the oxidation of the alloying element, particularly when tin is used as the alloying element.

Still another object of this invention is to produce a bright, gold deposit of heavy thickness having low internal stress.

Other objects of this invention will become clear as a result of the discussion hereinafter.

In the practice of this invention gold can be alloyed with any of the metals of Groups lI-B, III-B, lV-B, V-B and VI-B of the Periodic Table of Mendelyeev. In particular the alloying metals include cadmium, zinc, indium, lead, tin antimonium, arsenic, bismuth or selenium. The metals are added to the bath in quantities of up to about 100 g./l. The preferred ratio of the metal content is from about 1 g./l. to about 100 g./l. although lower amounts, e.g. .01 g./l., can also be used particularly when gold is alloyed with more than one other metal. In the latter event it is preferred to include the second metal in a lower quantity than the first metal, say from about 0.01 to 1.0 g./l.

As noted earlier, the preferred alloying metal is tin. It should be understood, however, that the other metals can be used in place of tin. Moreover, whenever tin-gold alloys are referred to hereinafter, it will be understood that such alloys are intended to include not only binary compounds, but also ternary and quaternary compounds are intended. In other words, gold-tin alloys include alloys of gold-tin and optionally one or more of the other metals of the groups of the Periodic Table mentioned above,

3,764,489 Patented Oct. 9, 1973 "ice especially the particular metals enumerated above, and most especially lead.

Heretofore, in the formation of gold-tin alloys, the industry faced the problem of preventing the oxidation of stannous ions to stannic ions. It is a natural phenomena that stannic ions do not codeposit from the plating solution. When tin is added in the form of stannous ions it oxidizes, on electrolysis of the solution, to the formation of stannic ions. Thus, more and more tin in the form of stannous ions must be added to the solution. The result is an extremely expensive bath due to the highconsumption of stannous ions and poor efliciency.

It has been discovered that the oxidation of stannous to stannic can be greatly minimized by using soluble tin anodes. The use of soluble tin anodes permits, for example, a significant reduction in the voltage across the terminals and can result in tin-gold alloys having as much as 50% by weight of tin.

When tin is used as the alloying metal, either alone or with another alloying metal, the electroplating composition of this invention will comprise from about 1 to about 100 g./l. of tin, preferably from about 1 to 40 g./ 1., added in the form of a stable stannous compound, e.g. stannous sulfate, stannous chloride, and from about 1 to about 30 g./l. of gold added to the plating bath in the form of a potassium gold cyanide. In addition, the plating bath will contain a complexing agentv which serves to complex with the stannous ions. The complexing agent can be any of the conventional complexing agents known to the art including weak complexing agents, including polyalcohols, e.g. glycerine or ethylene-glycol, and malic, maleic, lactic and gluconic acids and salts thereof. Most preferably, the complexing agent is gluconic acid and/or its salts. The complexingagents act as stabilizers and serve to increase the brightness. The complexing agent is present from about 5 to 500 g./l. with a preferred minimum amount of about 10 g./l. The baths are aqueous.

Preferably the alloying metals are tin and lead used together; the tin being present in amounts from about 1 g./l. to 100 g./l., preferably from about 1 to 40 g./l., and the lead in amounts from about 0.01 g./l. to 1.0 g./l. The gold alloy deposit obtained from this bath is bright. Such a deposit is not obtainable by alloying the gold with tin or lead individually.

The plating baths made as described herein can be electrolyzed and operated according to conditions known to the art, although the following conditions are preferred operating conditions: The preferred temperature range is from about 20 C. to about C. The preferred current density is from about 0.3 to about 2 A./dm. The preferred pH range is from about 3.5 to about 5.5.

The use of a diaphragm between the cathode and the anode is optional and may be helpful to prevent deposition of gold on the anode when the anode is of relatively low nobility, e.g. an anode of tin itself.

EXAMPLE 1 A bath was made up containing 10 g./l. of stannous sulfate, 20 ml./l. of sulfuric acid concentrated, g./l. of malonic acid, 8 g./l. of gold as potassium gold cyanide and 0.2 g./l. of antimonium as glycerollate. The pH was brought to 4.0 with potassium hydroxide. The current density was 0.5 A./dm. A soluble tin anode was used. Bright deposits were obtained of a thickness of 20 p.111. The deposits were of unusually low internal stress, exhibiting none of the usual characteristics of stress, e.g. cracking or crumbling. The efliciency of the plating bath was about 55 mg./A. min. The alloy deposit contained about 60% gold.

EXAMPLE 2 The same bath as in Example 1 was made up but 0.05 g./l. of arsenic as arsenic citrate was added in lieu of the glycerollate of antimonium. The bath was operated at a current density of 0.5 A./dm. Once more, bright, thick coatings of low internal stress, exhibiting none of the usual characteristics of internal stress were obtained. The efliciency of the plating solution was about 95 mg./A. min. and the alloy deposit contained about 75% gold.

EXAMPLE 3 A bath was prepared containing 20 g./l. of stannous chloride, 100 ml./l. of chlorhydric acid concentrated, 200 g./l. of malic acid, 10 g./l. of gold as potassium gold cyanide and 20 ml./l. of glycerine. The pH was brought to 4.5 with potassium hydroxide. A bright, tlick deposit showing no signs of internal stress was obtained. The plating bath efliciency was about 85 mg./A. min. at 0.5 A./dm. The alloy contained about 70% gold. It was later determined that the soluble tin anode used in this example contained small amounts of lead.

EXAMPLE 4 The same bath was used as in Example 3 but with one exception, 0.1 g./l. of lead nitrate was substituted for the glycerine. Bright, thick deposits were obtained once more showing none of the usual characteristics of internal stress. The efliciency of the plating solution was about 65 mg./ A. min at a current density of 0.5 A./dm. The alloy contained about 60% of gold.

EXAMPLE 5 A plating bath was prepared containing 5 g./l. of tin fluoborate, 120 g./l. of sodium gluconate and 4 f./l. of potassium gold cyanide. The pH was adjusted to 3.5 with fluoboric acid. Half bright, thick coatings of tingold alloy was obtained exhibiting none of the usual characteristics of internal stress. The alloy contained about 65% of gold. The eificiency of the plating bath was 80 mg./A. min. at a current density of 0.5 A./dm.

EXAMPLE 6' The plating bath as described in Example 5 was prepared and 110 g./l. of citric acid and 90 g./l. of potassium citrate was added. The bath was operated under the same conditions as in Example 5. Bright, thick coatings were obtained having low internal stress. The efliciency of the plating bath was about 60 mg./A. min. The alloy contained about 65% gold.

EXAMPLE 7 A bath was prepared containing 5 g./l. of antimonium chloride, 250 g./l. of gluconic acid, 60 cc./l. of chlorhydric acid concentrated, 40 cc./l. of glycerine and g./l. of gold as potassium gold cyanide. A soluble antimonium anode was used. The pH was adjusted to 5.0 by means of potassium hydroxide. Very good coatings, bright or half bright, according to the variations in the current density, and having practically no internal tension, were obtained. The efliciency of the plating bath was about 55 mg./A. min. at a current density of 0.5 A./dm. The alloy contained about 60% of gold.

EXAMPLE 8 The same bath as described in Example 7 was prepared with the further addition of 0.1 g./l. of bismuth chloride. Slight variations in current density gave significant variations in gold content. At a current density of about 0.5 A./dm. very good thick deposits of a yellow-grey tint were obtained. Those deposits exhibited virtually no internal stress. The efliciency of the plating bath was about 55 mg./A. min.

-It should be noted that in all of the examples mentioned above, the plating bath was operated at a temperature of about 45 C. to about 55 C. which is a preferred operating temperature. However, it should be understood that each of the above baths is operative at temperatures ranging from about 20 C. to about C.

It should be further understood that each of the above examples was intended merely to illustrate the invention and not to limit it. The particularities and characteristics of the invention as hereinabove disclosed will suggest to those skilled in the art further obvious modifications. It is, therefore, necessary that the annexed claims be construed in the context of the basic principles of this invention.

We claim:

1. A method for the electrodeposition of an alloy of gold with tin and lead onto a conductive surface which comprises immersing the conductive surface into an aqueous acidic plating bath comprising from about 1 to about 30 g./l. of gold as potassium gold cyanide, from about 1 to about g./l. of tin as a water soluble compound, from about 0.01 to about 1.0 g./l. of lead as a water soluble compound, and from about 5 to about 500 g./l. of a complexing agent for tin and electrolyzing said bath with said conductive surface as cathode.

2. The method of claim 1 where the complexing agent is a polyalcohol or is selected from the group consisting of malic acid, maleic acid, lactic acid, gluconic acid, and salts thereof.

3. The method of claim 2 wherein the amount of tin present ranges from about 1 to about 40 g./l.

4. The method of claim 3 where the pH of the bath ranges from about 3.5 to about 5.5.

5. The method of claim 4 wherein the complexing agent is gluconic acid or its salts.

6. The method of claim 1 wherein a soluble anode is used, said anode being made of a metal selected from tin or lead.

7. The method as described in claim 6 wherein a diaphragm is placed between the anode and cathode.

8. An aqueous acidic gold alloy plating bath comprising from about 1 to about 30 g./l. of gold as a water soluble gold cyanide, from about 1 to about 100 g./l. of tin as a tin and a water soluble compound, from about 0.01 to about 1.0 g./l. of lead as a water soluble compound, and about 5 to about 500 g./l. of a complexing agent for tin.

9. The bath of claim 8 wherein the complexing agent is selected from the group consisting of malic acid, maleic acid, lactic acid, gluconic acid, and salts thereof.

10. The bath of claim 9 wherein the water soluble gold cyanide is potassium gold cyanide.

11. The bath of claim 10 wherein the amount of tin present ranges from about 1 to about 40 g./l.

12. The bath of claim 9 wherein the complexing agent is gluconic acid or its salts.

13. The bath of claim 8 wherein the complexing agent is glycerine or ethylene glycol.

References Cited UNITED STATES PATENTS 1/1961 Ostrow et al. 204-43 OTHER REFERENCES GERALD LV.IKAPLAN, Primary Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,764,489 M October 9, 1973 Franco Zuntini et a1.

Patent No.

Inventor(s) identified patent It is certified that error appears in theaboveand that said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, after line8, insert Claims priority, application 1 Switzerland Nov. 28, 1968, 17,710/68 Sig he d and sealed this 3rd day of' December 1974 (SEAL) Attest: McCOY M. (mason JR. c. MARSHALL :DANN

Attesting Officer Commissioner of Patents uscomwbc '60376-P09 U,S. GOVERNMENT PR NTING OFFICE: 869- 3 F ORM PO-10SO (IO-69) 

